I want to maximize the number of available vehicles to reduce time

I am trying to solve a vrp which consists of pickups and deliveries. I have 73 vehicles and I want to use all the available vehicles to reduce overall time of process. I observed that the result is 24 vehicles never been used while other got multiple jobs. The issue is some of assigned vehicle actually come back to the next job at location that is nearer to unassigned vehicle while further to it last location. So looks like the engine still trying to use least vehicle. How could I change the parameters like:“FixedCost”,
to maximize the number of vehicles used? I have try to change some ways but still not working.